Mostly right, but only for light skin (and depends on the month and the latitude) (Table 1, Table 3). Dark skin usually needs 10-15 minutes (Table 2), and even 20 minutes for the darkest skin (Table 4). https://doi.org/10.3390/nu16101489

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kaikai 5 hours ago | parent [-]

I read the summary thoroughly and scanned the rest, and I don’t think the paper supports the grandparent comment.

The paper says you can produce enough vitamin d to maintain healthy levels from a specific amount of sunlight per day, depending on latitude and skin color.

The original comment suggests that there’s some (very short!) limit beyond which the body is unable to produce more vitamin d, which is very different. I’d be very curious to see sources for that.

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amavect 4 hours ago | parent [-]

Ah, I didn't read their comment too strictly.

UVB synthesizes cholecalciferol (vitamin D3) in the skin, which the liver converts into calcifediol (what blood tests usually measure), which the kidneys convert to calcitriol (the active hormone). Wiki claims the kidneys have a negative feedback loop, converting excess calcifediol into inactive 24,25-dihydroxycholecalciferol. I wish I had better sources (for my vitamin D pdf folder).

https://en.wikipedia.org/wiki/Vitamin_D#Excess

But just knowing that, I don't immediately see anything limiting cholecalciferol or calcifediol amount and storage.

	▲	plorg 4 hours ago \| parent [-]
		The same wiki article says there is a limit to the capacity of synthesis by UVB due to the quantity of reagent 7-dehydrocholesterol produced in the skin, but I don't know the math on what amount of exposure would be required to hit that limit - presumably it (or something like it) is covered in the article above.